Seals for semiconductor manufacturing devices are applied as surface seals that are used, for example, in process chambers for performing an etching process or for treatments, such as formation of thin films, on the surfaces of silicon wafers, which are semiconductor substrates. The seals are required to have heat resistance, low gas permeability, low dust characteristics (little generation of dust from seals), and other properties. In the etching process of silicon wafers, plasma irradiation is performed under the atmosphere of oxygen or CF4, and therefore the gas (oxygen or halogen) is excited. As a result, the seals for semiconductor manufacturing devices are vulnerable to deterioration; the surfaces of the seals become brittle; and the deteriorated materials and embrittled materials are dispersed and attached to the silicon wafers.
Meanwhile, in semiconductor manufacturing devices, cyano group-containing perfluoroelastomers and the like having excellent heat resistance are used to meet the demand for use of the seals at temperatures as high as 300° C. On the other hand, inorganic fillers, such as silica, barium sulfate, alumina, and aluminum silicate, are added to improve the plasma resistance. Although the addition of such inorganic fillers is effective in preventing the weight loss in the plasma irradiation environment, the presence of elements themselves, such as titanium, barium, aluminum, is undesirable in the semiconductor industry. For this reason, materials containing only silica or no inorganic fillers are preferred.
Moreover, when used for gate valves, the seals are required to be less adhesive, because strong adhesion to metal may cause defects.
As cyano group-containing perfluoroelastomers (fluorine-containing elastomers) having excellent heat resistance and usable in high-temperature environments in semiconductor manufacturing devices, and as vulcanizing agents thereof, those listed below have conventionally been proposed.
Known fluorine-containing elastomers have a copolymerization composition comprising (A) tetrafluoroethylene in an amount of 53 to 79.8 mol %, preferably 64.4 to 72.6 mol %, and more preferably 69.3 mol %; (B) perfluoro(methyl vinyl ether) in an amount of 20 to 45 mol %, preferably 27 to 35 mol %, and more preferably 30 mol %; and (C) a perfluoro unsaturated nitrile compound represented by the general formula:CF2═CF[OCF2CF(CF3)]xO(CF2)nCNwherein n is 1 to 4, and x is 1 to 2, in an amount of 0.2 to 2 mol %, preferably 0.4 to 1.0 mol %, and more preferably 0.7 mol %. Such fluorine-containing elastomers are supposed to be cured with a bisaminophenol or aromatic tetramine.    Patent Document 1: JP-B-2-59177
The present applicant has proposed vulcanizing this type of fluorine-containing elastomer using a bisamidoxime compound represented by the general formula:HON═C(NH2)—(CF2)n—C(NH2)═NOH, wherein n is 1 to 10, as a vulcanizing agent. Examples of fluorine-containing elastomers usable in this case include those having a copolymerization composition comprising (A) 45 to 75 mol % of tetrafluoroethylene, (B) 54.8 to 20 mol % of perfluoro(lower alkyl vinyl ether) or perfluoro(lower alkoxy-lower alkyl vinyl ether), and (C) 0.2 to 5 mol % of a perfluoro unsaturated nitrile compound. In the examples of Patent Document 2, fluorine-containing elastomers having a copolymerization composition in which the molar ratio of (A):(B):(C) is 63.5:34.9:1.6 or 68.8:30.0:1.2 are used.    Patent Document 2: JP-B-3082626
The present applicant has also proposed vulcanizing this type of fluorine-containing elastomer using a bisamidorazone compound as a vulcanizing agent. Examples of fluorine-containing elastomers usable here include those having a copolymerization composition comprising (A) 45 to 75 mol % of tetrafluoroethylene, (B) 50 to 25 mol % of perfluoro(lower alkyl vinyl ether) or perfluoro(lower alkoxy-lower alkyl vinyl ether), and (C) 0.1 to 5 mol % of a perfluoro unsaturated nitrile compound. In the examples of Patent Document 3, fluorine-containing elastomers having a copolymerization composition in which the molar ratio of (A):(B):(C) is 57.3:39.6:2.8 are used.    Patent Document 3: JP-A-8-119926
The fluorine-containing elastomer disclosed in Patent Document 2 has a cyano group that undergoes a crosslinking reaction with a bisamidoxime compound, which is used as a vulcanizing agent. A fluorine-containing elastomer composition prepared by compounding a vulcanizing agent with the fluorine-containing elastomer has a good processability, such as roll kneadability, and is expected to produce a vulcanization molded product having satisfactory heat resistance and solvent resistance; and the compression set values were measured at 275° C. or 300° C. for 70 hours. In terms of the compression set value at 300° C., however, the fluorine-containing elastomer is not considered to have heat resistance sufficient for use at temperatures as high as 300° C. in semiconductor manufacturing devices.